The weight of evidence for an extraordinary claim must be proportioned to its strangeness.
Interpretation
Extraordinary claims require substantial evidence to be accepted.
This quote by Pierre-Simon Laplace highlights the principle that the more unusual or extraordinary a claim is, the stronger the evidence must be to support it. It emphasizes a critical thinking approach to evaluating assertions, especially in scientific and rational discourse.
In practice
In a debate about the existence of aliens, one might use this quote to emphasize the need for solid evidence.
Without any doubt, the regularity which astronomy shows us in the movements of the comets takes place in all phenomena. The trajectory of a simple molecule of air or vapour is regulated in a manner as certain as that of the planetary orbits; the only difference between them is that which is contributed by our ignorance. Probability is relative in part to this ignorance, and in part to our knowledge.
It is interesting thus to follow the intellectual truths of analysis in the phenomena of nature. This correspondence, of which the system of the world will offer us numerous examples, makes one of the greatest charms attached to mathematical speculations.
All the effects of Nature are only the mathematical consequences of a small number of immutable laws.
The word 'chance' then expresses only our ignorance of the causes of the phenomena that we observe to occur and to succeed one another in no apparent order. Probability is relative in part to this ignorance, and in part to our knowledge.
Given for one instant an intelligence which could comprehend all the forces by which nature is animated and the respective positions of the beings which compose it, if moreover this intelligence were vast enough to submit these data to analysis, it would embrace in the same formula both the movements of the largest bodies in the universe and those of the lightest atom; to it nothing would be uncertain, and the future as the past would be present to its eye.
Probability theory is nothing but common sense reduced to calculation.
In any field, find the strangest thing and then explore it.
Any difficulties which the world faces today will be as nothing compared to the full effects which global warming will have on the world-wide economy.
To command their professors of astronomy to refute their own observations is to command them not to see what they do see and not to understand what they do understand.
Theory-free science makes about as much sense as value-free politics.
No new creation or destruction of matter is within the reach of chemical agency. We might as well attempt to introduce a new planet into the solar system, or to annihilate one already in existence, as to create or destroy a particle of hydrogen.
If two scientists are giving their papers at a symposium, and one of them is just naturally better at talking to the public or talking to a group of people, that scientist is liable to get more attention - in fact, I'm told that they do get more attention - than the one who's a little more stiff about it. Well, that's not good for science.
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